摘要
古大气CO_(2)浓度变化是驱动地球表面温度升高或降低的关键要素,也是我们解析地质历史时期冰室期和温室期气候状态转型的一个重要参数。现代海洋研究证实,海洋浮游植物及其产生的悬浮和沉降颗粒有机碳以及海底沉积物中有机质的碳同位素δ^(13)C值大小变化受到海水中溶解CO_(2)浓度控制,海水溶解CO_(2)碳同位素(δ^(13)C_(CO_(2)))与海洋来源有机质碳同位素(δ^(13)C_(org))的差值(Δ=δ^(13)C_(CO_(2))-δ^(13)C_(org)),与海水溶解CO_(2)浓度的倒数之间可以采用定量方程进行描述。如果引用海面古大气p CO_(2)与全球海表平均水温(GAT)相关方程,则可以通过海水溶解CO_(2)浓度定量计算海表古大气p CO_(2),同时求解古海洋平均海面温度和酸碱度pH值。四川盆地长宁县双河地区发育连续的奥陶系上部五峰组和顶部观音桥段以及志留系下部龙马溪组黑色泥页岩地层剖面,观音桥段的地层时代对应赫南特冰室期气候期。这一地表剖面生物化石控制精度高,岩石富有机碳,而且早古生代时期陆生高等植物尚未出现,这为我们采用海洋有机质碳同位素变化计算古大气p CO_(2)提供了最佳的材料。研究结果表明,观音桥段沉积期古大气CO_(2)浓度平均值为625μatm,海表全球平均温度为18.46℃,这些与新生代渐新世时期南极冰盖出现时冰室期气候状态可以对比。
Fluctuations in atmospheric CO_(2)concentration throughout geological history have been a pivotal driver of Earth’s surface temperature variations,serving as a key parameter for elucidating transitions between icehouse and greenhouse climates.Modern marine studies confirm that the carbon isotope composition(δ^(13)C)of marine phytoplankton,their derived particulate organic carbon,and sedimentary organic matter is primarily controlled by the concentration(or partial pressure)of dissolved CO_(2)in seawater([CO_(2)(aq)]).Previous work has established that the carbon isotope difference(Δ=δ^(13)C_(CO_(2))-δ^(13)C_(org))between seawater[CO_(2)(aq)]and marine organic matter exhibits a quantifiable relationship with the inverse of[CO_(2)(aq)].By incorporating an equation linking sea-surface atmospheric p CO_(2)to global average sea surface temperature(GAT),it is possible to estimate past atmospheric p CO_(2),mean sea surface temperature,and seawater pH.This study applies this approach to a continuous sedimentary succession spanning the Upper Ordovician Wufeng Formation,the Hirnantian Guanyinqiao Formation,and the Lower Silurian Longmaxi Formation.The Guanyinqiao Formation corresponds to the Hirnantian glaciation.This interval benefits from precise biostratigraphic age control,consists predominantly of organic-rich black shales,and was deposited prior to the emergence of terrestrial plants.Consequently,theδ^(13)C of its marine organic matter provides optimal material for reconstructing paleoatmospheric CO_(2).Our results indicate that during the deposition of the Guanyinqiao Formation,the average atmospheric p CO_(2)was approximately 625μatm,and the global average sea surface temperature was about 18.46℃.This climatic state represents an icehouse condition comparable to that during the Oligocene,following the establishment of the Antarctic Ice Sheet in the Cenozoic era.
作者
伊海生
伊帆
陈云
田康志
YI Haisheng;YI Fan;CHEN Yun;TIAN Kangzhi(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;College of Geography and Planning,Chengdu University of Technology,Chengdu 610059,China;Key Laboratory of Petroleum Resources Research,Gansu Province,Lanzhou 730000,China;Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences,Lanzhou 730000,China;Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《地学前缘》
北大核心
2026年第2期515-524,共10页
Earth Science Frontiers
基金
国家自然科学基金项目(42172121)
甘肃省油气资源研究重点实验室开放课题(SZDKFJJ2022002)。
